1. Field of the Invention
The present invention relates to a semiconductor device having a circuit composed of thin film transistors (hereinafter referred to as TFTs), a display device such as a light emitting device and a liquid crystal display device, and a manufacturing method of the same. Specifically, the present invention relates to the technique of pixel electrode periphery portion structures.
2. Description of the Related Art
A technique for manufacturing a TFT from a semiconductor thin film (with a thickness of between several hundreds to several thousands of nm) formed on a substrate having an insulating surface has recently been developed. In particular, since a TFT in which a polysilicon film (polycrystalline silicon film) is an active layer (hereinafter referred to as polysilicon TFT) has high electric field effect mobility, the thin film transistor is widely applied to semiconductor devices such as integrated circuits (hereinafter referred to as ICs) or electro-optical devices, and is needed to be developed promptly as, in particular, a switching element for a display device or the like.
For example, in a semiconductor device, a pixel portion for performing image displays on respective functional blocks, and an integrated circuit for controlling the pixel portion, (such as a shift register circuit, a level shifter circuit, a buffer circuit, or a sampling circuit which are based on a CMOS circuit) are formed on a single substrate.
Further, active-matrix liquid crystal display devices are frequently used as semiconductor devices because images with higher definition can be obtained compared to passive liquid crystal display devices. Also, the active-matrix liquid crystal display device includes: a gate wiring; a source wiring; a TFT in a pixel portion, which is provided at the cross point of the gate wiring and the source wiring; and a pixel electrode connected to the TFT in the pixel portion.
FIG. 8 is a cross section diagram of the pixel portion of a conventional semiconductor device. As in FIG. 8 in a conventional semiconductor device, a pixel electrode 804 was directly connected to a metal wiring 802 connecting a pixel TFT 805 and a metal wiring 803 connecting a storage capacitor 806.
However, an interlayer insulating film 801 contracts due to heat, and expands by containing water. Therefore, the following is confirmed: the wiring 802, 803 is likely to peel off the interlayer insulating film 801 to cause a shape defect of the wiring 802, 803; and the pixel electrode 804 is disconnected at a step portion of the wiring 802, 803.
FIG. 10 shows the above-mentioned defect of a wiring shape. FIG. 10 shows an image obtained by an SIM (Scanning Ion Microscope) with a magnification of 27,500 times. A wiring (Ti/Al/Ti) and a pixel electrode (made of an indium oxide—tin oxide (In2O3—SnO2) alloy (ITO)) are connected to the surface of an interlayer insulating film (made of acrylic resin). However, the wiring (Ti/Al/Ti) peels off the surface of the interlayer insulating film (acrylic resin). Along with this, the pixel electrode connected to the wiring (Ti/Al/Ti) is disconnected at the ends of the wiring (Ti/Al/Ti).
Disconnection of the pixel electrode at the ends of the wiring (Ti/Al/Ti) is one of the causes for a point defect of a semiconductor device.
There is also another problem. Due to the roughness of the upper surface of the interlayer insulating film, the pixel electrode on the interlayer insulating film is roughened to cause an alignment defect of liquid crystal molecules and a non-uniform electric field.
Furthermore, due to the roughness of the upper surface of the interlayer insulating film, the pixel electrode on the interlayer insulating film is roughened to cause a defect of the light-emitting device in which a minute defect occurs in the light-emitting layer laminated on the pixel electrode.